This invention relates to a device for tying cable bundles, consisting of a plastic tightening strap of indeterminate length having transverse ribs or serrations, and a separate locking piece or clip also of plastic, having an orifice through which the tightening strap leads and locking means projecting into the orifice and interacting with the transverse ribs or serrations on the strap to lock it in place.
Conventional tightening staps used for this particular purpose are produced by first extruding a strip of material that is smooth on all sides and then, in a subsequent operation, passing it through a pair of rollers, in which transverse grooves or serrations are formed on one flat side. To tie a cable bundle, this strap is pushed through the orifice of a locking piece in a direction counter to the locking surfaces of the locking means, and, after being wrapped round the cable bundle, is then guided back through the same orifice again but from the opposite side of the locking piece that faces the bundle, until the first transverse ribs on the strap engage with the locking means. The other end of the strap is then pulled back through the locking piece, until the cable bundle is wrapped tightly, and any undesired excess length of the strap is cut off. Thus, only an amount of tightening strap sufficient to wrap round the cable bundle is ever used.
Such a cable tie is shown, for example, in U.S. Pat. No. 3,744,096. As shown in FIG. 1 of the patent, the locking piece consists of two solid legs which are elastically connected to one another on their sides by means of flexible bridging webs to form a clip in the shape of a clothes pin, the legs of which have, at their shorter ends, opposed teeth that engage corresponding serrations on the tightening strap. The gap between the outer edges of the opposed teeth of the legs is set so that it is equal to or somewhat larger than double the thickness of the strap, measured from the bottom of the notches between the serrations. To pass the tightening strap through the clip, it is therefore necessary to first enlarge the gap somewhat. To permit this, the legs have to be pressed together with the thumb and index finger at the rear end of the legs opposite the ends having the teeth and facing the cable bundle, so that the tightening strap can pass through the widened gap between the engaging teeth. After the strap has been wrapped round the cable bundle, the legs have to be pressed together once again, so that the strap end, now looped round the bundle, can be guided back through the tooth gap a second time. This operation to set the clip is not only highly impractical, but also inconvenient.
In another embodiment as shown in FIG. 3 of this patent, the locking piece is composed of two parts, and includes a housing having an orifice for passage of the two ends of the strap that widens conically on both sides, and a wedge which can be pressed into the conical orifice from its open side to clamp the two ends of the tightening strap in the orifice.
In this embodiment, although it is no longer necessary to manually enlarge the gap to permit the ends of the strap to pass through the clip, it is nevertheless still necessary to press the wedge subsequently into place for locking purposes, with the result that this design is not only more complicated to handle, but is also more expensive to produce.
An object of the invention therefore is to provide a cable tie of the type having a serrated strap and locking clip where it is possible to pass the strap ends into the locking clip and lock the strap in place without any additional prior or subsequent manipulation of the engaging elements.